An engine may include one or more engine knock sensors to determine the presence or absence of engine knock in an internal combustion engine. The engine's cycle may total 720 crankshaft degrees and the engine's crankshaft cycle duration of 720 crankshaft degrees may be subdivided into one or more angular intervals where engine knock is expected to occur. These crankshaft angular intervals may be described as knock windows and there may be an individual and unique knock window for each cylinder of the engine. During a particular crankshaft interval where the knock window is described as “open,” output of an engine knock sensor may be sampled and processed to determine the presence or absence of engine knock associated with a particular engine cylinder. The same engine may from time to time operate with less than the actual total number of engine cylinders combusting fuel. Consequently, one or more engine knock windows may not be utilized because the cylinders that these knock windows are associated with are deactivated and cannot knock. However, the controller that generates these engine knock windows and the knock sensor sampling that is associated with the engine knock windows may still utilize controller resources to generate the knock windows and sample the knock sensor. Further, the controller may be constrained in a way engine background noise levels may be determined when the engine is operating because of legislated emissions and fuel economy. Therefore, it may be desirable to provide a way of determining engine background noise levels that improves controller processor utilization while mitigating effects of learning engine background levels on engine emissions and fuel economy.
The inventors herein have developed an engine operating method, comprising: deactivating a cylinder for one or more cycles of the cylinder via a controller; learning a base engine knock background noise level associated with the cylinder while the cylinder is deactivated; and adjusting engine operation according to a knock indication determined from the base engine knock background noise level.
By learning base engine knock background noise levels when one or more engine cylinders is deactivated, it may be possible to provide the technical result of learning engine knock background noise levels during engine operating conditions where the effect on engine emissions may be reduced. Further, the engine knock background noise level may be determined via a knock window that is not utilized to determine engine knock so that at least some benefit is provided by processor utilization for generating the knock window and processing output of the knock sensor.
The present description may provide several advantages. In particular, the approach may improve controller utilization during conditions when functions provided by the controller might otherwise be less useful. Further, the approach may capture engine background noise levels during a knock window that would otherwise not be utilized during an engine cycle. Further still, an engine background noise level captured via a knock window of one cylinder may be used to determine an engine background noise level for a different cylinder without having to adjust valve timings of the different cylinder to determine the background noise level for the different cylinder.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.